The field of solid state image sensors is well established. CCD and CMOS sensors are found in a large number of devices from digital still cameras to mobile telephones, as well as in laptops, webcams, pointing devices and barcode readers to name but a few. Mobile devices include, but are not limited to, mobile telephones, smart phones, palmtops and personal digital assistants, for example.
A typical camera module for a solid state image sensor is shown in FIG. 1. It includes a base 10, which can also be called a mount, and a barrel 12. In this example, the base 10 has a lower pedestal portion and an upper cylindrical portion which encases the barrel 12. A lens (not shown) is housed within the barrel 12, and the barrel moves vertically to adjust the focus. The lens 14 focuses incident light onto an image sensing integrated circuit 16, typically formed by a CMOS process. When packaging the camera module within a mobile device, it is important to protect the module and its components from being damaged by the end user or from entry of dust or other contamination. If the lens is exposed it can be scratched, and if the barrel 12 is exposed, any forces applied to it can make it move and interfere with the correct focusing of the camera module.
Traditionally, mobile devices have been constructed with a protective cover integrated into the casing to prevent damage and scratching to the camera module. However, with the abovementioned pressures on form factor and for other manufacturing reasons, some manufacturers prefer to omit this cover and leave the module exposed. In this case, a known way of protecting the module from exposure is to provide a circular glass or plastic fixture mounted on top of the barrel, usually fixed in place with an adhesive washer or with a glue material.
However, this method of protection presents a number of practical disadvantages. The fixture has a low mechanical strength when shear forces are applied, and forces applied to it will translate into the barrel and may move the focus of the module. Adhesive washers are a nonpermanent method, and can be peeled off by an end user. Glue and adhesive tend to be more susceptible to environmental conditioning, and do not perform well in drop tests. Furthermore, circular glass is relatively expensive compared to regular shapes such as squares or rectangles. This is due to the extra steps required to grind the edges, and to the material that is wasted in its manufacture.